There are several types of asphalts such as asphalt cement, liquid asphalt, and blown asphalt. Blown asphalt can contain oxidized asphalt which has higher softening point than non-oxidized asphalt. Blown asphalt is suitable for roofing, pipe insulation, sealing, and water-proofing.
Oxidation of asphalt to produce blown asphalt is generally conducted between 400 degrees Fahrenheit (deg F.) and 600 deg F. (204 degrees Celsius (deg C.)-315 deg C.) in the presence of flowing air. A catalyst such as phosphorous pentoxide and ferric chloride, can be added to facilitate oxidation.
Oxidation of asphalt includes many reactions. Major reactions are dehydrogenation, polycondensation, and coupling which leads to a product having higher molecular weight and higher softening point. The resin fraction of crude oil, which has more polar constituents than other fractions of crude oil, such as saturate, aromatics, and asphalthene) is easily polycondensed by oxidation.
The process to produce blown asphalt experiences slow mass transfer rates of gaseous oxygen into the viscous asphalt matrix that can limit the extent of oxidation. Catalyst can be used to increase the oxidation at low temperatures but catalysts increase the cost and require sensitive handling.
Asphaltenes can be used to produce blown asphalt. Unsaturated carbon to carbon bonds are more susceptible to oxidation than saturated carbon to carbon bonds. Common asphalt from conventional refining processes does not contain unsaturated bonds unless the refining process is a coker or other thermal cracking unit. However, asphaltenes from conventional thermal cracking units are not suitable feedstocks for blown asphalt due to the presence of solid coke in the asphaltene matrix.